Lubricant supply system and method for controlling gearbox lubrication

ABSTRACT

A lubricant supply system for a gearbox includes a lubricant flow circuit having, in fluid flow sequence: a variable-flow rate first pump; an lubricant cooler; and a gearbox. The system also includes: a first temperature sensor for sensing a temperature of lubricant circulating within the lubricant flow circuit; a pressure sensor for sensing a pressure of lubricant circulating within the lubricant flow circuit; and a controller operably connected to the pressure and temperature sensors and to the first pump. The controller is operable to control flow of the pump in response to the sensed temperature and to the sensed pressure.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to gearboxes. Other embodiments relate to lubrication of gearboxes subject to changing operational conditions.

A wind turbine includes a bladed rotor which drives a generator or alternator through a gearbox. The gearbox includes a number of gear meshes, bearings, and splines which require lubrication and cooling to remove the heat generated during operation. A conventional prior art wind turbine lubrication system includes an oil cooler and a pump with associated valves and piping configured to circulate cooled lubricating oil through the gearbox.

The gearbox requires maximum oil flow when it is operating at full mechanical load in high ambient temperatures. Under such conditions, the ambient and oil temperatures can be as high as 45° C. (113° F.) and 75° C. (167° F.), respectively. The same wind turbine may be exposed to conditions in which ambient air temperate is quite low, for example −30° C. (−22° F.), and little oil flow is required for cooling purposes.

It is known to provide a two-speed positive-displacement pump which has a maximum flow rate sufficient for the maximum required by the gearbox, and a lower flow rate which is approximately half of the maximum rate. However, at very low temperatures, high oil viscosity may result in very high pressures in which pump operation is not safe, even at the reduced speed. In these cases the only option to avoid damage to the gearbox and related components is to stop operation of the wind turbine.

Accordingly, there is a need for an oil supply system which protects gearbox components at widely varying environmental conditions, while maximizing the ability to generate electrical power under a wide range of ambient conditions.

BRIEF DESCRIPTION OF THE INVENTION

This need is addressed by die present invention, embodiments of which provide a gearbox lubrication system that controls flow through a lubricant flow circuit based on both temperature and pressure limitations.

According to one aspect of the invention, a lubricant supply system (e.g., for a wind turbine) includes a lubricant flow circuit having, in fluid flow sequence: a variable-flow rate first pump; a lubricant cooler; and a gearbox. The apparatus also includes: a first temperature sensor for sensing a temperature of lubricant circulating within the lubricant flow circuit; a pressure sensor for sensing a pressure of lubricant circulating within the lubricant flow circuit; and a controller configured to be operably connected to the pressure and temperature sensors and to the first pump. The controller is operable to control flow of the pump in response to the sensed temperature and to the sensed pressure.

According to another aspect of the invention, a method for controlling gearbox lubrication (e.g., for a wind turbine) includes: circulating lubricant at a flow rate through a lubricant flow circuit comprising a variable flow rate first pump, a lubricant cooler, and a gearbox; sensing a temperature of the lubricant, and varying the flow rate with reference to a lubricant temperature setpoint; and sensing a pressure of the lubricant, and varying the flow rate with reference to a lubricant pressure setpoint.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:

FIG. 1 is a partially-sectioned side view of a wind turbine including a gearbox and lubricant supply system constructed in accordance with an aspect of the present invention; and

FIG. 2 is a schematic of the gearbox shown in FIG. 1 with an associated lubricant supply system.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views, embodiments of the invention relate to a lubricant supply system (generally shown in FIG. 2), e.g., for a wind turbine. Other embodiments relate to methods for controlling gearbox lubrication, e.g., for a wind turbine.

FIG. 1 depicts a wind turbine 10 including a nacelle 12 mounted on the upper end of a tower 14. The tower 14 is anchored to the ground via foundations 16. A rotor 18 having blades 20 is mounted on one end of the nacelle 12. A rotor shaft 22 couples the rotor 18 to a gearbox 24, which is in turn coupled to a generator (or alternator) 26.

The gearbox 24, shown in FIG. 2, houses a multi-stage planetary gearset 28 of a known type (shown schematically). The gearset 28 is coupled to the rotor shaft 22 by an input shaft 30 located at an “upwind” end, and is coupled to the generator 26 by a pinion shaft 32 at a “downwind” end. In operation, the gearbox 24 functions to convert the relatively high torque, low speed rotational input from the rotor 18 (e.g., about 18 RPM) to a higher speed lower torque input suitable for operation of the generator 26 (e.g., about 1440 RPM).

Various parts of the gearset 28 are mounted in bearings, for example rolling element bearings. Several bearings 34 are shown schematically in FIG. 2. The bearings 34, along with the various gear meshes and splines in the gearset 28, generate heat during operation and require a flow of oil or other lubricant for cooling and lubrication.

A sump 36 (represented schematically as an open pan in FIG. 2) is positioned below the gearbox 24. Several drain lines 38 from various parts of the gearbox 24 empty into the sump 36.

A variable-speed electric motor 40 drives a first pump 42 which is connected to the sump 36 by a pick-up tube 44. The first pump 42 is a positive-displacement type pump. Its speed and volume flow rate varies with the speed of the motor 40.

In one embodiment, the lubricant supply system includes the first pump 42 only. In another embodiment, the lubricant supply system includes the first pump 42 and a second pump 46 that is mechanically driven by the gearbox 24. A pickup tube 48 feeds the second pump 46. The second pump 46 is a positive-displacement pump. Its speed and volume flow rate varies with the running speed of the gearbox 24. The first pump and the second pump are in effect coupled in parallel.

The combined discharge flow from the first pump 42 (and the second pump 46, if present) flows through a lubricant cooler 50 (e.g., oil cooler). The lubricant cooler 50 is of the air-to-lubricant type (e.g., air-to-oil type) and is provided with an electric fan 52. Flow exiting the lubricant cooler 50 supplies a lubrication manifold 54.

Distribution lines 56 emerging from the lubrication manifold 54 ran to various portions of the gearbox 24. Inside the gearbox 24, pressurized oil or other pressurized lubricant is distributed to various passages, lines, and nozzles and then pumped, sprayed, or otherwise supplied to the bearings 34 and gear meshes as required for cooling and lubrication. Collectively, the gearbox 24, sump 36, pumps 42 and 46, lubricant cooler 50, and lubrication manifold define a lubricant flow circuit. All of die components of the lubricant flow circuit are interconnected by appropriate piping, such as rigid or flexible tubes, with appropriate fittings and couplings.

Certain known elements common to lubricating systems are not shown in the figures and may be provided as part of a practical application of the lubricant flow circuit described herein. For example, the lubricant flow circuit may include one or more filters or screens, filter clogging sensors, check valves, pressure regulating and/or pressure relief valves, service or drain valves, and/or control valves.

At least one temperature sensor operable to generate a signal indicative of the lubricant temperature is provided. The lubricant temperature is indicative of the mechanical loads on the gearbox 24. Accordingly, the temperature sensor maybe placed in a physical location which is most sensitive to high temperatures or is likely to experience peak temperatures. In the illustrated example, a first temperature sensor 58 is positioned in the sump 36 immediately downstream of the drain lines 38, for sensing a first temperature of lubricant in the flow circuit, while a second temperature sensor 60 is positioned within the gearbox 24 for sensing a second temperature of lubricant in the flow circuit.

At least one pressure sensor 62 operable to generate a signal indicative of the lubricant pressure is provided. The pressure sensor 62 may be placed in a physical location which is most sensitive to high pressures or is likely to experience peak pressures. In the illustrated example, a pressure sensor 62 is positioned downstream of the discharge of the first pump 42.

A controller 64 is provided which is operable to control the speed of the motor 40 and the first pump 42 based on programmed control rules applied to the input signals from the temperature and pressure sensors 58, 60, and 62. As used herein, the term “controller” refers to any device capable of implementing programmed feedback control rules. Nonlimiting examples of suitable controllers include: hardwired circuit or relay logic, a dedicated proportional-integral-derivative (“PID”) controller, a programmable logic controller (“PLC”), or a general-purpose microcomputer. As used herein, the term “programmed” refers to software code, to hardwired logic, or to combinations thereof. The controller 64 incorporates in itself or is coupled to a suitable motor control device of a known type (not separately shown), such as a variable-frequency drive, a transistorized motor controller, or the like.

The speed of the motor 40 and first pump 42 (and thus the flow rate) is continuously variable between zero flow and the maximum rated pump output. The control rules incorporate both high and low limits. The gearbox 24 may be modeled as an open system in which heat is input by the gearset 28 and heat is removed by the flow of lubricant from the lubricant cooler 50. There is an established setpoint for the lubricant temperature. If the temperature setpoint is exceeded, this indicates the need for increased volume flow. The controller 64 responds by increasing the motor speed and volume flow rate. The increased flow rate of cool lubricant will eventually decrease the sensed temperature, at which time flow rate can be reduced. The lubricant flow rate is continuously governed in a feedback loop. Known control logic techniques such as FID control may be implemented by the controller 64 in order to provide rapid convergence with minimal overshoot in flow rate corrections. The controller 64 may also be programmed to govern the lubricant temperature with reference to the highest temperature sensed by the sensors 58 and 60.

In addition to the temperature setpoint, there is an established setpoint for the lubricant pressure. Because pressure increases with increasing viscosity for a given flow rate, exceeding die pressure setpoint indicates the need for decreased volume flow rate. The controller 64 responds to this condition by decreasing the motor speed and volume flow rate. The decreased flow rate of cool lubricant will decrease the sensed pressure, at which time flow rate can be increased. The lubricant flow rate is continuously governed in a feedback loop. Known control logic techniques such as FID control may be implemented by the controller 64 in order to provide rapid convergence with minimal overshoot in flow rate corrections. The pressure setpoint and corresponding flow rate may be selected so as to provide needed lubricant flow and permit power generation at low ambient temperatures, for example around −30° C. (−22° F.), and low mechanical loads, without causing damage and without opening any bypass or pressure safety valves in the system. In contrast to prior art practice, the flow rate may be a small percentage of the maximum possible flow rate, for example about 10%.

In an embodiment, the controller 64 is programmed to determine priority for lubricant flow rate control based on which parameter is closer to its established limit. In the unlikely situation that the sensed temperature and pressure should indicate the need for opposite corrections, the controller 64 may be programmed to control the lubricant flow rate based on the most critical parameter (for example a temporary moderate over-temperature condition may be considered more tolerable than an overpressure condition).

The system and method described above provide control of lubricant cooling and lubrication over a wide range of ambient and operating temperatures. In effect, the system implements a stepless transfer function to control maximum lubricant temperature and maximum lubricant pressure. These output variables can be programmed to any required value entered by a user. Compared to prior art methods, this will permit useful power generation in a wider range of conditions. In particular, it will allow useful power generation in very low ambient temperature conditions by limiting pump flow (and therefore lubricant pressure) to a level which is safe for operation without damaging components.

In an embodiment, the controller is programmed with a first setpoint and a second setpoint. The first setpoint designates a maximum lubricant temperature. The second setpoint designates a maximum lubricant pressure. The controller is operable to control the flow of the first pump in response to the sensed temperature and the sensed pressure in comparison to the first setpoint and the second setpoint, respectively.

In an embodiment, a lubricant supply system (e.g., for a wind turbine) includes a lubricant flow circuit having, in fluid flow sequence: a variable-flow rate first pump; a lubricant cooler; and a gearbox. The apparatus also includes: a first temperature sensor for sensing a temperature of lubricant circulating within the lubricant flow circuit; a pressure sensor for sensing a pressure of lubricant circulating within the lubricant flow circuit; and a controller configured to be operably connected to the pressure and temperature sensors and to the first pump. The controller is operable to control flow of the pump in response to the sensed temperature and to the sensed pressure. In another embodiment, the controller is operably connected to the pressure and temperature sensors and to the first pump, and is operable to control flow of the pump in response to the sensed temperature and to the sensed pressure.

An embodiment relates to a method for controlling gearbox lubrication. The method comprises circulating lubricant at a flow rate through a lubricant flow circuit comprising a variable flow rate first pump, a lubricant cooler, and a gearbox. The method further comprises sensing a first temperature of the lubricant, and varying the flow rate with reference to a lubricant temperature setpoint (e.g., the flow rate is varied based on comparing the first temperature to the temperature setpoint). The method further comprises sensing a pressure of the lubricant, and varying the flow rate with reference to a lubricant pressure setpoint (e.g., the flow rate is varied based on comparing the sensed pressure to the pressure setpoint).

In another embodiment, the method further comprises using a second pump disposed in parallel with the first pump and mechanically driven by the gearbox to circulate lubricant through the lubricant flow circuit.

In another embodiment of the method, the first temperature is sensed in the lubricant flow circuit downstream of the gearbox.

In another embodiment, the method further comprises circulating the lubricant through a sump disposed in the lubricant flow circuit between the gearbox and the first pump.

In another embodiment, the method further comprises sensing a second temperature of lubricant in the sump. The lubricant flow rate is controlled with reference to a higher of the first and second temperatures.

In another embodiment, the method further comprises using proportional-integral-derivative logic to control the lubricant flow rate.

In another embodiment of the method, the lubricant pressure is sensed in the lubricant flow circuit downstream of the first pump.

In another embodiment, die method further comprises determining a maximum lubricant flow rate referencing the lubricant pressure setpoint, and determining a minimum flow rate referencing the lubricant temperature setpoint.

In another embodiment, the method further comprises preferentially controlling the lubricant flow rate referencing either die lubricant pressure setpoint or the lubricant temperature setpoint depending on a predetermined priority.

In another embodiment of the method, the lubricant is circulated at a flow rate sufficiently low so that the lubricant pressure does not exceed the lubricant pressure setpoint.

In an aspect, with respect to a given point, “downstream” means away from the point in the direction of lubricant flow, and “upstream” means away from the point in the direction against lubricant flow.

The foregoing has described a system and method for controlling lubrication of a gearbox. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims. 

1. A lubricant supply system, comprising: a lubricant flow circuit comprising, in fluid flow sequence: a variable flow rate first pump; a lubricant cooler; and a gearbox; a first temperature sensor for sensing a temperature of lubricant circulating within the lubricant flow circuit; a pressure sensor for sensing a pressure of lubricant circulating within the lubricant flow circuit; and a controller configured to be operably connected to the pressure and temperature sensors and to the first pump, the controller operable to control flow of the first pump in response to the sensed temperature and to the sensed pressure.
 2. The system of claim 1 further comprising a second pump mechanically driven by the gearbox and coupled in the lubricant flow circuit in parallel with the first pump.
 3. The system of claim 1 wherein the first temperature sensor is disposed in the lubricant flow circuit downstream of the gearbox.
 4. The system of claim 1 further comprising a sump disposed in the lubricant flow circuit between the gearbox and the first pump.
 5. The system of claim 4 comprising a second temperature sensor disposed in the sump for sensing a temperature of lubricant in the sump, wherein die controller is operably connected to the second temperature sensor, the controller operable to control the flow of the first pump in response to the sensed temperature of the lubricant in the sump.
 6. The system of claim 1 wherein the controller is programmed with proportional-integral -derivative logic.
 7. The system of claim 1 wherein the pressure sensor is disposed in the lubricant flow circuit downstream of the first pump.
 8. The system of claim 1 wherein the controller is programmed with a lubricant temperature setpoint and a lubricant pressure setpoint, and the controller is operable to control the flow of the first pump in response to the sensed temperature and to the sensed pressure in comparison to the lubricant temperature setpoint and the lubricant pressure setpoint, respectively.
 9. The system of claim 8 wherein the controller is programmed to limit a maximum flow rate of lubricant through the lubricant flow circuit referencing the lubricant pressure setpoint, and to limit a minimum flow rate of lubricant through the lubricant flow circuit referencing the lubricant temperature setpoint.
 10. A method for controlling gearbox lubrication, comprising: circulating lubricant at a flow rate through a lubricant flow circuit comprising a variable flow rate first pump, a lubricant cooler, and a gearbox; sensing a first temperature of the lubricant, and varying the flow rate with reference to a lubricant temperature setpoint; and sensing a pressure of the lubricant, and varying the flow rate with reference to a lubricant pressure setpoint.
 11. The method of claim 10 further comprising using a second pump disposed in parallel with the first pump and mechanically driven by the gearbox to circulate lubricant through the lubricant flow circuit.
 12. The method of claim 10 wherein the first temperature is sensed in the lubricant flow circuit downstream of the gearbox.
 13. The method of claim 10 further comprising circulating the lubricant through a sump disposed in the lubricant flow circuit between the gearbox and the first pump.
 14. The method of claim 13 further comprising sensing a second temperature of lubricant in the sump; wherein the lubricant flow rate is controlled with reference to a higher of the first and second temperatures.
 15. The method of claim 10 further comprising using proportional-integral-derivative logic to control the lubricant flow rate.
 16. The method of claim 10 wherein the lubricant pressure is sensed in the lubricant flow circuit downstream of die first pump.
 17. The method of claim 10 further comprising determining a maximum lubricant flow rate referencing the lubricant pressure setpoint, and determining a minimum flow rate referencing the lubricant temperature setpoint.
 18. The method of claim 17 further comprising preferentially controlling the lubricant flow rate referencing either the lubricant pressure setpoint or the lubricant temperature setpoint depending on a predetermined priority.
 19. The method of claim 10 wherein the lubricant is circulated at a flow rate sufficiently low so that the lubricant pressure does not exceed the lubricant pressure setpoint. 